1-Pyrazolo pyrazine ring

Js.JJa.s in these systems is 0.5, indicating appreciable bond length alterations. 74.5 is very similar to 7o of benzene (9 Hz), while 75.6 is only 4.0 Hz. In the pyrazolo[l,5-fl]pyrazine ring system, H-6 and H-7 appeared at low fields (> 8.1 ppm), and Jej is only 5 Hz, indicating that bond order in these systems is less than in benzene (7o = 9 Hz) (74CPB1814). 

Only two isomeric pyrazolopyrazines are possible 1/f-pyrazolo [3,4- >]pyrazine (59) and pyrazolo[l,5-a]pyrazine (60). Derivatives of both ring systems are known. Annular tautomerism could occur in 59 [cf. 4 f-pyrazolo[3,4-( ]pyrazine (59a) ]. 

Only two reports have been found dealing with the chemistry of this ring system. In the first of these the amination of several simple pyrazine derivatives such as the dimethyl compound (1) with hydroxylamine O-sulfonic acid to give the corresponding iV-amino compounds is described. Treatment of the latter with derivatives of acetylenecarboxylic acid provides pyrazolo[l,5-a]pyrazines such as 2 in 2-10% yields. In contrast, the N-oxide of 1 gave a 41% yield of the 5-oxide 3. Condensation of the... 

Pyrazolo[3,4-fe]pyrazines have been the subject of a variety of reports dealing mainly with the synthesis and physical properties of the ring system. 

Pyrazolo[3,4-b]pyrazines are useful intermediates for the preparation of 2-aminopyrazine-3-carboxamides such as 49, much used in pteridine syntheses. For example, reductive cleavage of the 1-substituted 3-hydroxy compound 48 with Raney nickel results in smooth breakdown of the pyrazole ring to give the product 49. 

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